The problem of nondestructive measurement of composition with depth on the scale of ∼0.1–500 μm, in polymers and related materials, has many applications in traditional and recent areas of thin film processing. This article reviews the optical depth profilometry techniques operating on this scale based on optical absorption,photoluminescence, elastic, and inelastic scattering. These methods include photoacoustic and photothermal imaging (including pulsed laser opto–acoustic profiling), attenuated total reflectance infrared, integrated optical spectroscopy methods (based on excitation of planar waveguide structures), confocal scanning microscopy, and the recent technique of light profile microscopy. The profiling of planar structures is emphasized. A common element of all of these methods is that depth mapping requires the solution of a linear inverse problem, where a map of the sample properties is mathematically reconstructed from a set of experimental measurements. This problem is to some extent ill conditioned in some or all regimes of measurement, with the result that depth maps may show sensitivity to data errors. A method is presented for assessing performance of the above experimental depth profilometry techniques in terms of ill conditioning as indicated by: spatial resolution, sensitivity to data errors, and apparent multiplicity of solutions. This method is applied a priori given a knowledge of the linear response theory and measurement parameters Application is made to individual profiling techniques, the performance of each in applications is reviewed, and an inter-comparison is made based on the conditioning of the inverse problem.

We report on the frequency locking of a frequency doubled Nd:YAG laser to a 45 000 finesse, 87-cm-long, Fabry–Perot cavity using a modified form of the Pound–Drever–Hall technique. Necessary signals, such as light phase modulation and frequency correction feedback, are fed directly to the infrared pump laser. This is sufficient to achieve a stable locking of the 532 nm visible beam to the cavity, also showing that the doubling process does not degrade laser performances.

A compact apparatus for femtosecond pump–probe experiments is described. The apparatus is based on a cavity-dumped titanium:sapphire laser. Probe pulses are generated by focusing weak (∼1 nJ) pulses into a microstructure fiber that produces broadband continuum pulses with high efficiency. With the pump pulses compressed and probe pulses uncompressed, the rise time of the pump–probe signals is <100 fs. The 830 nm pump pulses are also frequency doubled to generate light for excitation at 415 nm. The versatility of the spectrometer is demonstrated by exciting molecules at either 830 or 415 nm, and probing at wavelengths ranging from 500 to 950 nm. Some results on the green fluorescent protein are presented.

A laser-pump, x-ray probe spectroscopicexperiment is described, and the results are shown. The Ga x-ray fluorescence following x-rayabsorption, at the Ga K absorption edge was measured, and its increase due to excitation with subpicosecond pulses of laser light at 4.6 eV photonenergy was determined. The x-rayabsorption, and thus the fluorescence, is increased for about 200 ps after the laser pulse because additional final states for the x-rayabsorption are cleared in the valence band by the laser excitation. The technique could eventually lead to a femtosecond pump-probe spectroscopy with an absolute reference energy level and also to a femtosecond x-ray detector. This is of particular importance to future short-pulse x-ray sources, such as free-electron lasers.

A new synchrotron radiation undulator beamline, SGM2, with an energy range of 12–20 eV, has been commissioned on the ASTRID storage ring at the University of Aarhus. Using a spherical gratingmonochromator, the beamline is presently optimized for an energy of 15.76 eV (78.65 nm), for the resonance in argon, for use in electron-molecule scattering experiments. Using this beamline in conjunction with an electron-molecule scattering apparatus, a beam of electrons down to kinetic energies of a few meV with a resolution of ∼1 meV full width at half maximum is routinely produced.

A module was constructed for the measurement of deep sea optical activity at a sensitivity level of a single photoelectron. We describe the features of the module and a method for calibrating it. The average sensitivity in the interval from 350 to 500 nm is 0.89 Hz/(photons where Hz is the rate detected by the module.

We have narrowed the spectral bandwidth of a commercial 2 W laser diode array to be less than 120 MHz near 780 nm. The external-cavity laser diode array system is a standard double-pass Littman–Metcalf configuration operating on a dominant single longitudinal mode.

The influence of a metal–dielectric (MD) cylindrical structure, covering the radial walls of the plasma chamber of an electron cyclotron resonanceion source (ECRIS), on the production of highly charged ions is discussed. Its influence on the main plasma parameters (plasma potential, electron density, and electron temperatures) was investigated using the Langmuir probe method. An increase of these parameters was observed when the MD structure was inserted into the plasma chamber of the Frankfurt 14 GHz ECRIS. In addition, the plasma potential was measured independently by determining the offset extraction voltage at zero magnetic field of the magnetic 90° analyzer field with high precision. Good agreement with the Langmuir probe results was obtained. The main influence of the MD structure is characterized by a significant increase of the plasma potential. This indicates that the MD structure helps to increase lifetimes of both, electrons as well as ions. The ion lifetime is known to be one of the essential parameters to influence the production of highly charged ions.

A comprehensive characterization of experimental parameters in a study of proton acceleration by short-pulse laser–solid interactions at intensities up to is reported. Laser pulse and prepulse conditions were measured, with a contrast ratio of the order of obtained. The focused laser intensity was experimentally calibrated using a time-of-flight spectrometer to resolve the stages of ionization of a target gas. By comparing the measured ion yields with predictions of an atomic tunnelingionization model a factor of 1.5 uncertainty in the focused intensity was determined. Drive mechanisms for mounting solid targets with thickness in the range of 0.2 to 125 μm have been developed for use with high-repetition rate lasers. A retro-focus imaging system has also been implemented to position the target relative to the laser focus. The techniques have been applied to study proton acceleration as a function of various laser and target parameters. Measurements of the energy distribution of protons as a function of laser intensity are presented for both mylar and Al targets. A maximum proton energy of 1.5 MeV was observed. A compilation of recent results from a number of laser systems on the conversion efficiency of laser energy to protons is discussed. By comparison, an efficiency of about 0.7% for the present study is encouraging for future tabletop-laser-based ion acceleration.

We describe an ion cyclotron resonance (ICR) mass spectrometer that we have built. The design of the instrument was guided in large measure by theoretical consideration; in particular we wished to investigate the effects of improved electrostatic linearity on ICR performance. We found, for instance, that the trap’s performance as a mass spectrometer is essentially independent of the trapping potential. By studying both cyclotron and magnetron modes we were able to characterize both the trap and the magnet. Further, we were able to separate effects of image charge from space charge; this gave us measurements of ion number and ion cloud shape. Finally, we show that the instrument readily provides accurate mass measurements with minimal calibration.

We describe the design and characterization of a high resolution, high efficiency detector for two-dimensional imaging of neutral atoms. Incident atoms are surface-ionized by a tungsten-coated hot ribbon and the resulting ions are accelerated into a microchannel plate detector with a phosphor screen output. With this design we can detect individual alkali and other low ionization potential atoms and molecules with a spatial resolution of We find backgrounds on the order of 30 Hz over an active detection region of a time response of and a detection efficiency of This detector can be used to image cold as well as thermal atomic or molecular beams.

We illustrate the use of a three-dimensional charge-coupled-device (CCD)camera detection system in an ion imaging experiment. The time measurement is based on the decay characteristics of the phosphor screen, which is recorded in two successive images by a double exposure CCDcamera. The strength of the method is illustrated in a velocity map imaging experiment on iodine molecules that are ionized and dissociated by intense femtosecond laser pulses. Singly and doubly charged iodine fragments are detected and their coordinates and arrival time are recorded in an event counting routine. We estimate the time resolution of the system to be 1.3 ns. We show that the fragment velocity distribution derived from the data is similar and in some conditions more accurate than the distribution obtained by a mathematical inversion of the data only. This principle of detection can be used in all situations in which inversion methods are impossible, for example, when the particle distribution does not have an axis of symmetry.

Three-dimensional optical random access memory (3D ORAM) materials with enormous capacity and fast access speed have shown a great potential in overcoming limitations of access and storage capacity in current memory devices. As another useful development of this 3D ORAM, we have shown the application of 3D ORAM materials as a practical dosimeter. The local heating of the polymer matrix by the deposited energy of ionizing radiation is thought to contribute to the conversion of the fluorescent photochromic dye to a nonfluorescent form. The two-photon readout system is very useful in tracking the interactions of energy of ionizing radiation deposited in a polymer matrix. However, the polymerfracturing that has occurred during two-photon readout has been an obstacle in utilization of 3D ORAM materials as a dosimeter. In this work, we further evaluated the readout system using a high-energy variable attenuator in order to prevent polymerfracturing due to the strong absorption of the 1064 nm beam by the polymer matrix. Through adjustment of the 1064 nm beam intensity using this attenuator, two-photon excited fluorescence of anthracene-doped 3D ORAM materials could be obtained without polymerfracturing. As a result of this improved procedure, a highly spatially resolved fluorescence image of anthracene-doped 3D ORAM material could be observed with the two-photon readout system.

A modified plasma-synthesis method is developed in order to actively control an ion flow energy along magnetic-field lines, where ion and electron emitters of the same diameter are oppositely set at cylindrical machine ends and the ion emitter is concentrically segmented into three sections. The field-aligned ion flows with radially different energies, or ion flow velocity shears, are generated in a radially uniform plasma potential when each section of the segmented ion emitter is individually biased at a positive value above the plasma potential.

In this article, we demonstrate through calculations and theoretical analysis the first application of an x-ray laser for probing hot, high-density plasmas using a Ni-like transient collisional excitation x-ray laser as a probe. Theoretical predictions are used to diagnose the electron temperature in short-pulse (500 fs) laser-produced plasmas. The threshold power of the x-ray probe is estimated by comparing theoreticalscattering levels with plasma thermal emission. The necessary spectral resolution of the instrument sufficient for resolving electron temperature is given. Effects of the electron heat flow on the ion-acoustic fluctuation spectra are presented. The outlook for these and next generation experiments are discussed.

A microwaveimaging system based on a heterodyneinterferometer has been developed to measure the spatial distribution of the plasma density without introducing any direct disturbance to the plasma by employing a diode array scattering technique. The imaging system with the use of a fan beam microwave for a radar system demonstrates the principle of the technique by placing finite-size dielectric phantoms instead of the plasma between the horn antenna and the diode antenna array. Experimental results show that very good image of the objects can be reconstructed and the system is equivalent to popularly known multichannel imaging system. As a result, it is possible to make simple, low-cost, and compact microwaveinterferometer for measuring the spatial distribution of the plasma density.

A probe method for measurement of the ion energy distribution in magnetized plasmas is proposed. A cylindrical probe with end plugs is oriented parallel to the magnetic field and used to reduce the electron contribution to the total probe current. The contribution of ions to the second derivative of the total current is identified by experiments with different probe orientation and strength of the magnetic field. The ion density obtained from the measured ion energy distribution is in good agreement with the electron density obtained from measured electron energy distribution.

This article describes a diagnostic for measuringneutron emission profile in JT-60U. The Stilbene neutrondetector, developed by TRINITI laboratory in Russia, has been installed on the JT-60U Tokamak to measure the neutron emission profile for the first time. The Stilbene neutrondetector is a detector which combines a Stilbene crystal scintillator with a neutron-gamma pulse shape discrimination circuit, with a very compact size. Performance tests were carried out using neutron and gamma-raysource prior to installation on JT-60U. Good gamma suppression of the Stilbene neutrondetector was verified. Though the neutron emission profile obtained by Stilbene neutrondetectors has error of 30% in innermost channel with a calculation using measuredplasma parameters, there is an agreement within 10% error in the other channels.

A diagnostic technique based on sets of CdTe detectors is used for measurements of spatial localization and temporal evolution of the nonthermal up to 150 keV) x-ray emission in plasma with high density in the T-10 tokamak. Various types of x-ray bursts observed during the density limit disruption appear as a result of the forward bremsstrahlung due to nonthermal electron interaction with the residual plasma as well as to nonuniform interaction of the runaway electrons with the plasma-facing constructions.

An x-raymicrotomography method combined with hard x-ray imagingmicroscopy was developed that has a potential spatial resolution of the order of 10–100 nm. The system consists of a high-brilliance undulator source of SPring-8, a beam diffuser plate to reduce the coherence of the illumination, a high-precision rotating sample stage, a Fresnel zone plate objective, and a high-resolution x-ray imaging detector. The three-dimensional images of several samples were observed and successfully reconstructed with a pitch pattern of 0.6 μm.